Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.84	10.284%	$39.5258	$39.53	$39.55	$39.50
Purchase #2	$48.94	8.250%	$52.9776	$52.98	$53.00	$53.00
Purchase #3	$78.50	3.596%	$81.3229	$81.32	$81.30	$81.30
Purchase #4	$134.86	5.807%	$142.6913	$142.69	$142.70	$142.70
Purchase #5	$224.37	10.686%	$248.3462	$248.35	$248.35	$248.30
Purchase #6	$238.53	6.763%	$254.6618	$254.66	$254.65	$254.70
Purchase #7	$101.46	4.368%	$105.8918	$105.89	$105.90	$105.90
7 purchase totals =	$862.50		$925.4174	$925.42	$925.45	$925.40